A loading space shall have minimum dimensions of not less than twelve feet in width, fifty feet in length, exclusive of driveways, aisles and other circulation areas, and a height clearance of not less than fifteen feet. One off-street loading space shall be provided and maintained on the same lot for every separate occupancy requiring delivery of goods and having a modified gross floor area of up to 5, 000 square feet. One loading space shall be provided for each additional 10, 000 square feet or fraction thereof.